Defining DSL in Ruby

Transcript

1. Defining DSL in Ruby
   TRUG 17/06/15
   

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2. Michal Poczwardowski
   Ruby on Rails developer
   michal.poczwardowski@netguru.co
   dmp0x7c5@gmail.com
   

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3. DSL
   Domain Specific Language
   

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4. DSL
   INTERNAL
   ● just embedded in GPL
   (General Purpose Language)
   EXTERNAL
   ● own parser/lexer/syntactic
   tree
   ● examples: SQL
   

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5. Examples from Ruby world
   ● rspec
   ● factory-girl
   ● chef
   ● sinatra
   ● AR migrations
   

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6. Why?
   ● easy to read
   ● easy to use by non-programmers
   ● in Ruby… easy to implement!
   

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7. Potential project
   ● DSL for defining online surveys
   ● All questions specified just using a DSL instead of
   complicated forms
   

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8. Survey DSL
   01: survey :trug_questions do
   02: title 'A few questions about TRUG'
   03: question :city, kind: :single_choice do
   04: text 'Where do you live?'
   05: answer_option :gdansk
   06: answer_option :gdynia
   07: answer_option :sopot
   08: end
   09: end
   

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9. Result
   

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10. How?
    

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11. Question + QuestionBuilder
    Question = Struct.new(:text, :answer_options)
    class QuestionBuilder
    def initialize
    @text = 'Unset Text'
    @answer_options = []
    end
    def build
    Question.new(@text, @answer_options)
    end
    end
    

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12. QuestionBuilder
    class QuestionBuilder
    def text(content)
    @text = content
    end
    def answer_option(label)
    @answer_options << label
    end
    end
    

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13. instance_eval
    def build_question(&block)
    builder = QuestionBuilder.new
    builder.instance_eval(&block)
    builder.build
    end
    build_question do
    text 'Where do you live?'
    answer_option :gdansk
    answer_option :gdynia
    answer_option :sopot
    end
    

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14. It may be a string
    def build_question(dsl_string)
    builder = QuestionBuilder.new
    builder.instance_eval(dsl_string)
    builder.build
    end
    build_question "
    text 'Where do you live?'
    answer_option :gdansk
    answer_option :gdynia
    answer_option :sopot
    "
    

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15. Result
    --- !ruby/struct:Question
    text: Where do you live?
    answer_options:
    - :gdansk
    - :gdynia
    - :sopot
    

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16. docile gem
    Docile turns any Ruby object into a DSL.
    Especially useful with the Builder pattern.
    

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17. docile gem
    01: with_array([]) do
    02: push 1
    03: push 2
    04: pop
    05: push 3
    06: end
    #=> [1, 3]
    def with_array(arr=[], &block)
    Docile.dsl_eval(arr, &block)
    end
    

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18. Resources
    https://en.wikipedia.org/wiki/Domain-specific_language
    https://robots.thoughtbot.com/writing-a-domain-specific-language-in-ruby
    http://ms-ati.github.io/docile/
    http://radar.oreilly.com/2014/04/make-magic-with-ruby-dsls.html
    

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19. Thanks!
    

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